The employment of magnetoresistive (MR) elements as sensors for electromagnetic transducers has led to improved performance of heads for disk and tape drives. As is well known, the resistance of an M element varies according to the magnetic field impinging upon the element, so that flowing an electric current through the element can be used to determine that magnetic field by measuring the change in resistance.
While bulk materials may exhibit some MR effect, such effects generally become more pronounced as an element becomes smaller relative to the applied electrical and magnetic flux. Thus it is known that films formed of materials such as Permalloy, which is an alloy of nickel and iron having a high permeability and low coercive force, are useful as sensors for heads when the film thickness is less than about 500 .ANG.. Even thinner films exhibit quantum mechanical effects which can be utilized in devices such as spin valves for MR sensing. Higher storage density associated with smaller bit size also requires smaller MR elements.
Generally speaking, the thinner the film used for MR sensing, the more important that the film have a uniform thickness and structure. As such, the material surface or template upon which the film is formed is important. Heads for hard disk drives commonly include an MR sensor in a gap region located between or adjacent to a pair of magnetically permeable layers that are used for writing signals onto a disk. The conventional material forming the gap is alumina (Al.sub.2 O.sub.3), which is known to be easy to form and work with, and which provides suitable template for forming thin MR films. Alumina, however, has a strong affinity for moisture and tends to form a columnar molecular structure, which is porous, both of which can undermine the quality and integrity of an adjoining MR sensor.
MR elements are also sensitive to a change in temperature, as such a change typically leads to a change in resistance, which can be misinterpreted as a change in magnetic flux or false signal. Thermal asperities caused by ephemeral contact between a head and disk, for example, can cause such signal errors, and for this reason it can be advantageous to thermally isolate an MR sensor. Higher magnetoresistance also generally implies increased heat generation by an MR film, however, and thus greater temperature increases during operation of the sensor. This higher operating temperature can also be deleterious to reading of signals.